Norman Ramsey, who shared the 1989 Nobel Prize in physics for his research into atomic energy levels that led to the creation of the atomic clock and MRI machines, has died.

Dr Ramsey died in his sleep at a nursing home near Boston in the US, his wife Ellie Ramsey said today. He was 96.

Dr Ramsey, an emeritus professor of physics at Harvard University and longtime Brookline resident, wrote in his autobiography for the Nobel Prize he shared with Hans Dehmelt and Wolfgang Paul that he was inspired by failure in molecular beam magnetic resonance experiments in the late 1940s to invent a new technique of measuring the frequency of radiation from atoms using two electromagnetic fields.

The technique is known as the "separated oscillatory fields method", or more informally among physicists, the Ramsey method, said his protege and longtime friend Daniel Kleppner, a physics professor emeritus at the Massachusetts Institute of Technology.

It was used in the hydrogen maser, developed to measure the effect of gravity on time. It led to the development by others of the world's most accurate timekeeper, the cesium atomic clock.

Since 1967, the second has been defined as the time during which the cesium atom makes 9,192,631,770 oscillations.

Dr Ramsey, after his Nobel win in 1989, called it a "valuable application" that has been used in radio astronomy, satellite navigation, space exploration and to test the theory of relativity.

His research also led to invention of the MRI machinery now used extensively in medicine, Dr Kleppner said.

"His work has had a broad impact, and his concepts are pervasive," he said.

After learning he had won the Nobel Prize, Dr Ramsey said that he attributed his long interest in science to the fact that "it's fun".

"Basically, I'm interested in all the laws of nature," Dr Ramsey said at the time.

He was born in Washington DC, his mother a college mathematics teacher and his father a West Point military academy graduate and career army officer.

Dr Ramsey said he developed an interest in physics at a young age when he read an article on the quantum theory of the atom.

He graduated from high school at the age of 15 and because he could not follow his father's footsteps and attend West Point because he was too young, enrolled at Columbia University in 1931.

During the Second World War, he contributed to the war effort by working on radar projects at the Massachusetts Institute of Technology, and as a radar consultant to the secretary of war, ultimately working on the Manhattan Project that developed the atomic bomb.

He helped establish the Brookhaven National Laboratory in New York after the war, before joining the Harvard faculty in 1947, where he taught until 1986.

"He was exuberant, outgoing, friendly, incredibly energetic and inquisitive," said Dr Kleppner, Dr Ramsey's graduate student at Harvard in the 1940s. "But above all he had tremendous scientific integrity and honesty."

His wife remembered him for his sense of humour, his penchant for adventurous travel and his love of sports and the outdoors.

He developed a lifelong love of skiing while visiting Norway in the 1930s, which he passed on to his children and grandchildren. He even took up surfing in his 50s.

His first wife, Elinor, died in 1983. In addition to his wife, he is survived by six children and stepchildren, eight grandchildren, and nine great-grandchildren.